Progress report for FNE23-060
Project Information
This project seeks to:
- Demonstrate a new way to supplement naturally recruiting seed on mussel farms to help grow mussel aquaculture in Maine.
- Compare more expensive industry-standard fuzzy rope and recycled lobster rope for their ability to recruit mussel pediveligers in a remote settlement tank, then ultimately how the ropes will each perform on the farm. This can identify potential cost savings for farmers and optimize the remote settlement process.
- Determine the stocking density per tank that will result in optimum settlement - lines stocked with ample seed, but not so many that the ropes will need to be stripped later on and the seed reattached to new lines at a lower density, as can happen in a natural set. This will help improve efficiency and reduce costs.
The US imports 32,000 metric tonnes of mussels, mostly from PEI as well as New Zealand, Vancouver and Chile. A bottleneck in Maine’s rope-grown mussel industry is the traditional reliance on mussel spat settling from the wild onto collector ropes. When a few Maine farmers recognized more variable natural settlement on their farms eight years ago, they approached Downeast Institute to see if an affordable hatchery alternative to natural settlement could be developed. The solution DEI developed consists of suspending ropes in tanks of sea water into which hatchery-spawned “eyed” pediveligers (larval mussels that are developing a foot and are nearly ready to settle from the water column onto a surface) are introduced. This technology enables farmers to receive supplemental seed if needed to mitigate variable settlement, or to increase production on their farm by staggering rope deployment beyond the natural season imposed by nature.
While Bangs Island is eager to benefit from this technology, the capacity of DEI to produce seeded mussel ropes is limited, and results will vary by farm. Through this project, Bangs Island could provide a “proof of concept” in Maine for on-farm or remote settlement. The results are intended to help shield mussel farms from the uncertainty of natural settlement which has been created by climate change, and help increase productivity on a farm using the same lease footprint it already occupies. Once Bangs Islands Mussels understands optimal rope type and stocking density, we will know how to use the remote settlement process most economically and with the greatest production impact. This knowledge will be transferred to other farmers to benefit the whole industry.
Cooperators
- - Technical Advisor
Research
Trial 1. Rope type
Using the right type of rope is important to the success of a mussel farm. Some mussel farmers prefer commercial fuzzy rope made specifically for mussel farming, while others use discarded lobster pot warp (polypropylene rope). We will conduct a trail at Bang’s Islands Mussel’s land based facility in Portland, Maine in May of 2023. to determine which type of rope has the best spat retention on our farm when the rope is seeded in our remote settlement tanks. We will place six PVC racks, each housing 50 meters of continuous rope and a one meter test rope, into each of four 1,000L remote settlement tanks. Two of the tanks will hold fuzzy rope and two tanks will receive used lobster pot warp. These tanks will be run as flow-through, fed by a common head tank in which filtered seawater is heated and buffered to adjust pH to 8.2. The head tank will also be used for feed dispersal. A 120 micron banjo filter in each settlement tank will allow water to overflow while retaining the larvae. Each tank will receive fresh seawater at a rate of one gallon per minute. Tanks will each be aerated to evenly disperse larvae. 6,000,000 viable mussel pediveligers produced in DEI’s hatchery will be added to each tank at the start of the trial.
Two weeks after the introduction of larvae, the racks will be removed and the sample ropes from each rack will be subsampled by cutting three 2-3 cm sections of rope to determine initial mussel density. The racks will be labeled and deployed on Bang’s Island mussel rafts in Casco Bay. Half of the ropes from each treatment will be deployed on an open water production raft and the other half will be deployed on the special mussel nursery raft. The remote settlement tanks will be drained onto a 120 micron sieve and the number of dead mussel larvae will be enumerated to help determine recruitment success.
The labeled mussel ropes suspended from the farm’s rafts will be monitored monthly by lifting two ropes from each remote settlement tank at random and photographing them. 20 mussel seed will be removed from each rope and measured to establish a growth curve over the growing season. At the end of the growing season (October 2023) the ropes will be removed from the rafts and the mussel seed will be stripped from each rope. The total weight of seed from each rope will be recorded and 20 live mussels from each subsample will be measured for further analysis.
Once all data is collected, we will analyze it to determine which rope type resulted in the highest initial density prior to deployment and at the end of the growing season. We will also examine differences in growth between rope types. This information will help us determine which rope type will lead to higher yield in a remote settlement scenario at our farm.
Trial 2. Density
Mussel farmers often find themselves with too many mussel seed on their settlement ropes in years when wild recruitment is high. The density of the seed must then be reduced by stripping the seed from the ropes and resocking it, at a proper density, onto growout ropes. This process is very labor intensive and costly to the farmer. If hatchery reared mussel larvae can be settled onto growout ropes at a proper density it may allow the farmer to skip this step in the husbandry process.
To test what initial density of mussel juveniles results in the most efficient yield of market product we will set up a trail at Bang’s Island Mussel’s facility. We will place six PVC racks, each housing 50 meters of continuous fuzzy rope and a one meter sacrificial test rope, into each of four 1,000L remote settlement tanks as above. 6,000,000 viable mussel pediveligers will be added to each of two tanks (High Density) and 3,000,000 mussel pediveligers will be added to the other two (Low Density) at the start of the trial (Figure 2). Tanks will be monitored and banjo filters will be cleaned twice a day.
Two weeks after the introduction of larvae, the racks will be removed and the sample ropes from each rack will be subsampled by cutting three 2-3 cm sections of rope for later determination of initial mussel density. The racks holding ropes will be labeled and deployed on Bang’s Island mussel farm in Casco Bay. Half of the ropes on each treatment will be deployed on an open water production raft and the other half will be deployed on the special mussel nursery raft. The remote settlement tanks will be drained as above to determine recruitment success.
The labeled mussel ropes suspended from the mussel rafts will be monitored as above. 20 mussel seed will be removed from each rope and measured to establish a growth curve over the growing season. At the end of the growing season (October 2023) the ropes from the high density treatment will be removed from the rafts and the mussel seed will be stripped from each individual rope. The yield from each rope will be measured by taking ten subsamples that are weighted and the number of live mussels recorded. The total weight of seed from each rope will be recorded and 20 live mussels from each subsample will be measured for further analysis. The seed will then be resocked onto growout ropes and suspended from the raft. The ropes from the lower density treatment will be photographed and 20 mussels from each rope will be measured. These ropes will remain in their current condition.
The mussels should reach a harvestable size by November of 2024. At that time the mussels will be harvested and the total weight of harvested product from each rope will recorded and subsamples will be taken to determine how many mussels were produced from each rope. 20 mussels from each rope will be measured at random and meat yields will be taken from each animal.
Once all data is collected, we will analyze it to determine which initial density resulted in the most efficient yield of product after 18 months. We will also determine which density produced mussels with the highest meat yield. This information will help us determine which initial density will produce a more efficient yield of market product in a remote settlement scenario at Bang’s Island Mussel.
Trial 3. Nursery Step
A nursery step may be necessary to allow the recently settled mussel larvae to securely attach to the growing ropes before being deployed on open ocean growing sites. Nursery sites have lower wave energy which may allow the mussel to create a stronger bond to the lines. The nursery and non-nursery trials detailed above will determine the necessity of this step. Update: Do to a lack of suitable nursery sites near Portland, the nursery trials were cancelled.
Trial 4. Repeat
At the end of August, 2023 the treatment that is currently showing the most promise will be repeated by Bangs Island Mussels without the aide of the Technical Advisor. This will further reinforce the results and demonstrate the ability of farmers to use the technique without more technical assistance.
Update: Do the the high occurrence (near 100% of trial lines) of line tangles and wild mussel overset, all treatments will be repeated. Special care will be payed to predicting and avoiding wild mussel sets and line lengths will be adjusted to avoid tangles.
As of the beginning of 2024, each trial will need to be repeated due to a high occurrence of wild mussel overset and line tangles. The wild mussel oversets made the hatchery mussel trials impossible to interpret. The tangles of the lines stripped off the mussels from the lines.